Which parts fail
Components named in complaints (accelerator pedal, throttle, sudden acceleration, cruise control).
Mileage when the problem started
Owner reports
Selected complaints filed with NHTSA by 1998 Mercury Mountaineer owners, lightly cleaned up (personal details are redacted by NHTSA).
Under my hood started smoking, I popped my hood to find flames under it. I had to get my kids out the truck and put the flames out with and extinguisher. That's when I noticed that my brake fluid reservoir was melted and so were the wires that connect to the cruise control switch. Not I am without a vehicle to get to work and get my children to school.
Dt*: the contact stated the vehicle erupted in flames, an hour and a half after it had been parked in the carport. The contact's house became engulfed in flames and was a total loss. The fire department responded and there was a police report taken. The insurance company and manufacturer inspected the vehicle. The insurance company was unable to come to a final determination about the fire, but stated it looks as though the fire started in the vehicle speed control area. The vehicle was deemed a total loss by the insurance company. There is a NHTSA recall, # 05V388000, regarding the vehicle speed control. The vehicle has the same problems as indicated in the recall; however, it is not included in the recall due to the VIN.
When the 1998 Mercury Mountaineer was running on hwy 121 south merging into hwy 114 west in grapevine, tx, the 1998 Mercury suddenly became out of control at a speed less than speed limit. The car was being accelerated even if the accelerator pedal was off. The driver applied break to stop the car but the break did not work. Then the driver had to steer the car into the bush off road to avoid collision to other cars. The driver changed the at to p (parking) to stop the car. The engine surged and started fire underneath of the car. Then the driver removed the key and evacuated from the car. The fire was extinguished by the fireman.
When the 1998 Mercury Mountaineer was running on hwy 121 south merging into hwy 114 west, the 1998 Mercury suddenly became out of control at a speed less than speed limit. The car was being accelerated even if the accelerator pedal was off. The driver applied break to stop the car but the break did not work. Then the driver had to steer the car into the bush off road to avoid collision to other cars. The driver changed the at to p (parking) to stop the car. The engine surged and started fire underneath of the car. Then the driver removed the key and evacuated from the car. The fire was extinguished by the fireman.
Drove about 30 minutes, parked vehicle, and about 45 minutes later vehicle was on fire. Flames were coming from driver's side fender well. Prior to fire, no problems reported. Vehicle had cruise control which was not used in the last year, and did not know if it worked. Vehicle was insured by farmers insurance. They had a fire investigation done. The report stated that fire was caused by vehicle speed control deactivation switch. Policy #0040483408, claim #1005487896. Has pictures and them will e-mail to bruce york.
Dt*: the contact stated while the vehicle was being inspected by an independent repair shop it caught on fire. A report was filed by the fire department. The mechanic determined the fire was caused by the cruise control switch over heating. The vehicle is currently awaiting the replacement parts for the cruise control and surrounding damaged parts. There is a NHTSA recall, # 99V062001, regarding the cruise control. The VIN was not included in the recall.
Tl* - the contact stated that while her 1998 Mercury Mountaineer was parked, the contact heard a loud noise coming from her vehicle. She noticed that her vehicle had flames coming from under the hood. The fire department arrived and extinguished the fire. The contact feels that the cause of the fire was due to NHTSA campaign id number : 00V422000( vehicle speed control). The contact can provide pictures, as well as, copy of the incident report.
Dt*: the contact stated the vehicle caught fire and burned. The vehicle was parked 4 hours prior to the fire. The fire and police department stated in written reports the fire started in the engine compartment on the driver's side. Additional property damage was sustained to one other vehicle. The insurance company investigated and deemed the vehicle a total loss.
While turning right through a cloverleaf interstate entrance ramp at approximately 35-40 MPH I attempted to accelerate and merge with on-coming traffic. The accelerator pedal popped and went under the brake pedal. I was able to pull to the side of the road and visually verified that the accelerator pedal bracket had broken. This is the metal bracket that was spot welded to the cowl panel/("firewall"). This left 3 holes in the cowl panel, each being approximately 7/32" in diameter. I was able to drive the vehicle home by pulling the accelerator pedal towards me until I was above 30 MPH, then I controlled the speed using the cruise control. I was out of my home state when this occured, and because of my location at the time of failure I was forced to drive the vehicle in this condition for 3 hours. …
I have been having problems with throttle sticking upon depression on 1998 5.0 Mercury Mountaineer. Seems to be worse when first starting vehicle or when the temperature outside is colder. Last night when I left to go to work, I put the vehicle in drive, the throttle stuck and I could not control the vehicle. I struck my own home doing considerable damage to the home (passenger side of vehicle) , bounced off the house (still accelerating) and hit a garbage dumpster (driver side of vehicle) , then bounce off the garbage dumpster and struck a basketball goal (front of vehicle). The airbags did not deploy (this is the 2nd front end accident in which airbags did not deploy). This throttle body problem was a recall for the 4.0 vehicles but not the 5.0, and I have seen numerous complaints of throttle sticking on the 5.0 as well. Vehicle is now in the shop, believed to be a total loss. …
Related recalls
Vehicle speed control
Vehicle description: sport utility vehicles equipped with 4.0l sohc engines and still retain the original throttle body (part numbers 97jf-9e926ab or 97jf-9e926-ac). Some of the original throttle bodies installed allowed a gap between the plate and bore to be built too narrow.
Remedy: Dealers will replace the original throttle bodies.
Vehicle speed control
Vehicle description: certain 1997-1999 rhd explorer equipped with 4.0l ohv/sohc engines and cruise control built from May 29, 1996 through March 4, 1999; 1998-1999 explorer/mountaineers equipped with 4.0l ohv/sohc or 5.0l engines or 1998-1999 rangers equipped with 2.5l, 3.0l ffv/efi or 4.0l engines and cruise control built from…
Remedy: Dealers will replace the cruise control cables. At the present time, the replacement cables are not available. Customers are being advised not to use the cruise control system until a replacement can be made.
Acceleration complaints in other Mountaineer years
Frequently asked questions
How common are acceleration problems on the 1998 Mercury Mountaineer?
NHTSA has 36 complaints about the speed control & acceleration of the 1998 Mercury Mountaineer, 15% of the model year's 236 complaints. The component named most often is accelerator pedal (13 mentions).
Is there a recall for 1998 Mercury Mountaineer acceleration problems?
Yes — NHTSA recall 00V-422 (vehicle speed control, Dec 27, 2000); NHTSA recall 99V062001 (vehicle speed control, Mar 30, 1999). Recall repairs are free at authorized dealers.
At what mileage do 1998 Mercury Mountaineer acceleration problems start?
Half of the complaints with a recorded mileage happened before about 100,000 miles, and 6% before 25,000 miles.
Is it dangerous?
Owners linked 7 crashes, 9 fires and 5 injuries to speed control & acceleration problems on this model year. If you notice symptoms, have the car checked before driving further.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.